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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 181628

Area Forecast Discussion
National Weather Service San Diego CA
928 AM PDT Sat May 18 2019

Dry and warmer weather today, then cooler and breezy on Sunday as
a cold front approaches and moves onshore. Showers and an isolated
thunderstorm are expected. The snow level will lower down to 6000
ft, with several inches possible above 8000 ft. Winds will become
quite gusty into the deserts. Continued breezy and cool on Monday
with showers ending early over San Diego County. Another large, 
cold trough develops over the West by Tuesday and slowly weakens 
through Friday. It will maintain strong onshore flow, with below 
normal temperatures, a deep marine layer, and a chance for more 
light precipitation midweek. 



At 9 AM, water vapor satellite showed an upper-level low around
450 miles west of the northern CA coast, with weak ridging over
southern CA. Warmer, yet still below normal high temperatures will
develop today, with dry weather. The aforementioned low will move
inland across central CA by the end of the weekend, with a cold
front moving across southern CA Sunday. Increased onshore flow
will create gusty westerly winds for inland areas, especially over
the mountains and deserts, on Sunday. This system is looking to 
have enough instability for shower development across most of the 
area, and with a deep layer of lower-level moisture present, which
will also help showers develop inland and along the mountain 
slopes. CAPE of 400-800 J/kg will also help isolated thunderstorms
develop, mainly over the coastal waters Sunday morning, then over
the mountains in the afternoon. 

Rainfall amounts are expected to be one-quarter inch or less along 
the Coast, to one-half to one-and-one-half inches in the mountains 
where upslope flow and a threat for heavier convective showers 
exists later in the day. Several inches of snow could accumulate 
above 6500-7000FT in the San Bernardino and San Jacinto Mts and 
strong and gusty westerly winds will develop Sunday afternoon and 
evening in the mts/deserts. A Wind Advisory will likley be needed 
and perhaps even a Winter Weather Advisory if QPF remains on

The airmass moving in Sunday will be quite cold for this time of
year, with high temperatures expected to be 20 to 35 degrees F
below seasonal normals for inland areas. Several locations are 
expected to break their lowest high temperature record at times 
Sunday through Wednesday.

Only a small break in the active weather is expected late Monday
through early Tuesday, then another system moves inland with a
trough moving across southern CA mid-next week. The enhanced 
onshore flow and deep marine layer generated by this system once 
again threatens accumulating precip along and west of the
mountains and gusty winds for inland areas.

Looking ahead to the upcoming holiday weekend, the 
operational and ensemble means for the ECMWF/GFS still favor a 
trough over the SW. It looks weaker with less cold air, so the 
weather may be dry with temps closer to average.


181500Z...Coast/Valleys...Expect an absence of low clouds today, 
with high clouds AOA 20000 FT MSL. SCT to locally BKN low clouds 
could redevelop on the coast after 05Z, but will likely remain 
patchy through about 12Z Sunday, after which OVC low clouds with 
variable bases AOA 2500 FT MSL will surge inland to the mountains.
-SHRA starting near 13Z at KSNA and KONT, progressing from NW to 
SE through the morning into early afternoon. -SHRA chances will be
greatest near noon at KSAN. Rain will exit the area in the 
afternoon. Local vis 3-5 mi in heavier showers will be possible. 

Mountains/Deserts...VFR will prevail through Sunday morning. OVC 
skies and SHRA will affect the mountains after 19/15Z, with 
strengthening west winds after 18Z Sunday and likely MOD-STG UDDFTS 
and LLWS over and east of the mtns. 


Hazardous boating conditions are expected over the next few days. 
Locally gusty west winds this evening, especially over the Outer 
Waters, but will remain below Small Craft Advisory criteria. Winds 
will strengthen further late morning on Sunday, when a front will 
generate some showers, and persist into Monday. Expect frequent 
gusts to 25 kts, and even 30 kts at times over the Outer Waters. A 
Small Craft Advisory will likely be needed. 

High seas are also expected, with combined seas of 10 to 13 feet 
over the Outer Waters, and 8 to 10 feet over the Inner Waters Sunday 
night and into Monday.

Winds will remain gusty through at least Tuesday, but conditions 
should improve for the second half of the week.  


Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.